System

Radiochemistry Laboratory for a UK Nuclear Dockyard v2 — continuing first-pass decomposition. Prior sessions decomposed Active Ventilation and Containment System (7 components) and Radiation Protection and Health Physics Monitoring System (6 components). This session tackled the {{entity:Active Effluent Treatment and Discharge System}}, the third subsystem and highest-risk undecomposed element due to its environmental release potential and regulatory burden under Environment Agency RSR permits and nuclear site licence LC34.

Project now at 88 requirements (31 SUB, 18 IFC, 19 VER, 5 ARC, 10 SYS, 5 STK), 32 PART_OF facts, 23 CONNECTS facts across 3 decomposed subsystems. 8 top-level subsystems remain undecomposed.

Decomposition

The AETDS was decomposed into six components reflecting the real batch effluent processing chain of a nuclear dockyard radiochemistry facility:

1. {{entity:Active Drain Collection Network}} {{hex:CE851019}} — gravity-fed and pumped 316L SS/borosilicate glass piping collecting radioactive liquid waste from fume cupboards, glove boxes, and sinks across controlled areas.

2. {{entity:Inactive Drain Diversion System}} {{hex:54B63250}} — separate non-active drainage with continuous flow-through gross gamma detectors and motorised divert valves that route contaminated flows to the active system within 5 seconds.

3. {{entity:Effluent Collection and Delay Tanks}} {{hex:CE953259}} — four 5000L stainless steel tanks in a fill-sample-hold-discharge cycle with 24-hour minimum hold for short-lived isotope decay, double-contained in 110% bunded enclosures.

4. {{entity:Batch Sampling and Analysis Station}} {{hex:55E75018}} — automated peristaltic sampling with on-line pH, conductivity, temperature, and gross gamma screening via NaI scintillation. LIMS interface via OPC UA for batch disposition decisions.

5. {{entity:Chemical Treatment Plant}} {{hex:54D53259}} — pH neutralization (NaOH/HNO3), ferric floc co-precipitation for actinides (DF ≥100), and mixed-bed ion exchange for Cs-137/Sr-90 removal (DF ≥10). ILW sludge packaged in 200L drums for the Radioactive Waste Management Facility.

6. {{entity:Discharge Monitoring and Control System}} {{hex:55F77A51}} — SIL 2 PLC-based control with ZnS alpha and plastic scintillation beta-gamma in-line monitors, electromagnetic flowmeters (±1%), and fail-safe pneumatic discharge valve closing in <5 seconds on high activity, signal loss, or power loss.

flowchart TB
  ADCN["Active Drain<br/>Collection Network"]
  IDDS["Inactive Drain<br/>Diversion System"]
  ECDT["Effluent Collection<br/>and Delay Tanks"]
  BSAS["Batch Sampling<br/>and Analysis Station"]
  CTP["Chemical<br/>Treatment Plant"]
  DMCS["Discharge Monitoring<br/>and Control System"]
  LIMS["LIMS"]
  RWMF["Radioactive Waste<br/>Management Facility"]

  ADCN -->|Active liquid waste| ECDT
  IDDS -->|Diverted contaminated drain| ECDT
  ECDT -->|Sample lines| BSAS
  ECDT -->|Effluent for treatment| CTP
  CTP -->|Treated effluent return| ECDT
  ECDT -->|Authorised batch| DMCS
  BSAS -->|Batch disposition| ECDT
  BSAS -->|Screening results| LIMS
  CTP -->|ILW sludge drums| RWMF
  DMCS -->|Discharge records| LIMS

The architecture decision {{stk:ARC-REQ-005}} records why batch-mode processing was selected over continuous flow-through: every batch must be characterised before discharge per EA permit conditions, and the single discharge point enables a simple SIL 2 fail-safe isolation architecture.

Analysis

The {{entity:Discharge Monitoring and Control System}} shares ontological traits (Powered, Observable, Active, Rule-governed, Regulated, System-Essential, Ethically Significant) with the {{entity:Process Safety System}} from the offshore oil platform decomposition. Both are SIL-rated safety instrumented systems protecting against environmental release through fail-safe final elements. The key architectural parallel is the principle that the discharge/isolation safety function must be independent of the batch management control system — a common-cause failure in the control PLC must not defeat the safety function.

The {{entity:Chemical Treatment Plant}} hex code {{hex:54D53259}} shows strong State-Transforming and Temporal traits alongside Regulated and Ethically Significant, reflecting its nature as a batch chemical process under environmental regulation. The Effluent Collection and Delay Tanks {{hex:CE953259}} uniquely carry the Temporal trait among the AETDS components, correctly reflecting the 24-hour decay hold as an intrinsic time-dependent function.

Lint returned 2 high findings (CAM network and ventilation system lacking Physical Object trait) and 2 low findings. The ventilation finding was previously acknowledged in session 326. The CAM network finding was acknowledged this session as ontologically correct for a distributed sensor network. The low finding on “shall” keywords in ARC and VER entries is expected — these are architecture decisions and verification procedures, not testable requirements.

Requirements

10 subsystem requirements created ({{sub:SUB-REQ-022}} through {{sub:SUB-REQ-031}}), covering delay tank hold time, capacity, containment, chemical treatment decontamination factors, sampling representativeness, SIL 2 discharge isolation, flow measurement, inactive drain diversion, material compatibility, and ILW sludge management.

6 interface requirements ({{ifc:IFC-REQ-013}} through {{ifc:IFC-REQ-018}}) define the drain-to-tank, tank-to-sampling, tank-to-treatment, discharge-to-site, sampling-to-LIMS, and treatment-to-waste boundaries with specific flow rates, bore sizes, data protocols, and acceptance criteria.

7 verification entries ({{sys:VER-REQ-013}} through {{sys:VER-REQ-019}}) including a system-level integration test ({{sys:VER-REQ-018}}) exercising the complete batch cycle from waste introduction through treatment to authorised discharge. The SIL 2 proof test ({{sys:VER-REQ-015}}) tests all three trip conditions for the discharge isolation safety function.

5 trace links from {{sys:SYS-REQ-003}} to derived subsystem requirements, plus 6 IFC-to-VER verification traces. All session-328 requirements confirmed to have rationale.

Next

8 subsystems remain: Radioactive Waste Management Facility, Facility Safety and Emergency Response System, Sample Receipt/Registration/Preparation, Radiochemical Separations Laboratory, Laboratory Information Management System, Laboratory Utilities and Building Services, and the three analytical suites (Alpha Spectrometry, Gamma Spectrometry, Liquid Scintillation Counting). Next priority should be the Radioactive Waste Management Facility — it receives ILW sludge from the Chemical Treatment Plant and solid waste from all laboratories, and its interface with AETDS needs to be formalised from the receiving end.